1. Field of the Invention
This invention relates to an apparatus and a method of making an optical lens such as a contact lens or an intraocular lens having an aspherical shape such as a toric shape, a bifocal shape or a prism shape.
2. Discussion of Background
Conventionally, in the field of optics, especially a field of a lens for an eye in the eye science, an optical lens having an aspherical shape such as a toric shape, a bifocal shape or a prism shape, other than a simple spherical lens, is required for a contact lens for correction of astigmatism or the like.
As for a method of making such aspherical lens, conventional various methods have been proposed. For instance, in Japanese Examined Patent Publication No. 2742/1988, a method of making a toric shape lens is proposed, in which a roughly machined lens blank is deformed in compression (in bending) in the radial direction. Under such condition, the surface thereof is machined in a spherical shape by a cutting bit while the lens workpiece is driven to rotate around an axis. Furthermore, in Japanese Unexamined Patent Publication No. 27813/1988, the lens workpiece is driven to rotate around a plurality of rotating axes. By cutting the surface thereof in a spherical shape by a cutting bit around the respective rotation axes, a lens of a bifocal shape is produced.
However, in the former method shown in Japanese Examined Patent Publication No. 12742/1988, the lens workpiece is forcibly deformed, which applies an unfavorable influence on the lens workpiece such as strain or the like. Therefore, it is difficult to obtain a lens product of high quality. Furthermore, in the latter method shown in Japanese Unexamined Patent Publication No. 27813/1988, it is extremely difficult to control to change the rotation axis of the lens workpiece. Therefore, it is difficult to stably obtain a lens product having a required optical property, since the variation caused in the final lens shape is considerable.
Furthermore, in the specification of the U.S. Pat. No. 4,884,482, a lens workpiece is rotated around an axis by a rotating member holding the predetermined lens workpiece. The surface of the lens workpiece is cut to a desired shape, by contacting a predetermined cutting bit to the lens workpiece, and by swinging the cutting bit around an axis orthogonal to a rotation axis of the rotation member. On such occasion, a rotation angle of the rotation member and a swing angle of the cutting bit are detected. Synchronizing with the rotation angle of the rotation member, the rotation member is reciprocated toward and away from the cutting bit, by a predetermined quantity corresponding to the swing angle of the cutting bit, by which an aspherical lens is produced.
However, to obtain an economical cutting speed of the lens workpiece which is cut by the cutting bit, it is necessary to rotate the rotation member at the rotation speed of at least 1,000 r.p.m., preferably at least 3,000 r.p.m. Therefore, for instance, in making a lens of a toric shape, the rotation member should be reciprocated at the rate of at least 2,000 times/min. Therefore, it is necessary to install a driving device having extremely large output, to reciprocate the rotation member having a rotation driving mechanism, at such high rate. The control thereof is extremely difficult. The axial vibration due to the rotation is easily to be amplified by the reciprocation, which makes an accurate control difficult. Therefore, in such method of making an aspherical lens, it is not possible to obtain a sufficient productivity, and the reduction to practice thereof is extremely difficult.